The present invention relates to a carburetor for supplying mixtures of gasified fuel and air into an internal combustion engine, and more particularly to a carburetor for use in a so-called torch-ignition type internal combustion engine comprising a main combustion chamber and an auxiliary combustion chamber maintained in communication with said main combustion chamber through a small port.
In general, the torch-ignition type internal combustion engine comprises a main combustion chamber to which a lean mixture of gasified fuel and air is supplied and an auxiliary combustion chamber maintained in communication with said main combustion chamber through the small port and to which a rich mixture of gasified fuel and air is supplied. The flames of combustion created in the auxiliary combustion chamber by igniting the rich mixture of gasified fuel and air supplied into the auxiliary combustion chamber, in turn ignite the lean mixture of gasified fuel and air which is supplied into the main combustion chamber, thereby integrally operating the engine by using the lean mixture of gasified fuel and air.
With a view to the improvements of the fuel consumption rate and the decrease of nitrogen oxide and the like in quantities in the construction of the torch-ignition type internal combustion engine, the volume of auxiliary combustion chamber may be preferably smaller than that of main combustion chamber, and for example, the volume of auxiliary combustion chamber is practicable to be at 3 to 4% of that of main combustion chamber.
A carbureter for supplying mixtures of gasified fuel and air into the torch-ignition type internal combustion engine of the type described must accurately control the flow of mixtures of gasified fuel and air to be supplied, Particularly, an accurate control is required for a throttle valve of the auxiliary carbureter supplying the rich mixture of gasified fuel and air into the auxiliary combustion chamber having an extremely small volume as compared with that of main combustion chamber, as described above.
There have heretofore been used butterfly valves as the throttle valves in carburetors in general. In case that a butterfly valve of the type described is used in the auxiliary carbureter supplying an extremely small quantity of mixture of gasified fuel and air into the auxiliary combustion chamber of the torch-ignition type internal combustion engine, the mixture of gasified fuel and air is greatly affected by air leakage around the periphery of the valve. Thus, the butterfly valve is not suitable as the throttle valve for the carburetor used in the auxiliary combustion chamber of the torch-ignition type internal combustion engine.
In this respect, there has recently been proposed a carburetor in which the air leakage around the periphery of a valve is minimized by a provision of a rotary throttle valve provided therethrough in the radial direction of the rotary shaft with a gasified fuel-air mixture passageway, thereby permitting the accurate control of the flow of mixtures of gasified fuel and air.
However, with a view to construction, a low speed bypass mechanism of the carburetor having a butterfly valve cannot be utilized in the aforesaid carburetor having a rotary throttle valve. Thus, a characteristic for feeding combined fuels from a low speed fuel system and a main fuel system is not favorable, so that there occurs a phenomenon in which the flow rate of fuel is not smoothly increased and the mixture becomes lean in a transient operating condition of the internal combustion engine in which the main fuel system starts to operate. In other words, a combined fuels feeding characteristics is favorably carried out in the carbureter using the butterfly valve, because the low speed bypass mechanism operates in accordance with an opening of the butterfly valve, but, in the case of a rotary throttle valve, the conventional bypass mechanism does not operate, even if the rotary throttle valve is open, thus resulting in an unfavorable combined fuel feeding characteristics. As the result, an ignition plug provided in the auxiliary combustion chamber fails to ignite the mixture of gasified fuel and air in the auxiliary combustion chamber, which in turn leads to any failure in igniting the mixture of gasified fuel and air in the main combustion chamber. Thus, such problems are presented that favorable rotation of the engine cannot be obtained, and unburnt combustible components of carbon monoxide, hydrocarbon and the like increase which are contained in exhaust gases.